1. Field of the Invention
The invention pertains to a piston-cylinder unit consisting of a working cylinder; a piston attached to a piston rod and installed with freedom of axial displacement in the working cylinder; and fastening elements, at least one of which is screwed into a threaded bore in the piston rod, where the interior pressure in the working cylinder holds a valve in the bore of the piston rod against an end surface of the fastening element, and where a vent bore leading to the atmosphere is provided between the end surface and the valve to create a pressure gradient to the working space.
2. Description of the Related Art
U.S. Pat. No. 6,223,649 discloses a piston-cylinder unit in which an axially movable piston is provided in the working cylinder, where at least one of the fastening elements is screwed into a threaded bore in the piston rod and holds a valve of a pump rod complex in place in the axial direction, as shown in FIG. 5.
Self-pumping hydropneumatic spring strut units with internal level control are also known (e.g., DE 33 16 069 C2), in which a control sleeve and a snap ring are used to install a valve of a pump-rod complex in the hollow space inside the piston rod, and in which a stopper, which is a component of a fastening element, is used to hold the valve in its axial position in one direction. This pressure valve is held in its axial position in the other direction by the positive pressure in the working space, because this positive pressure is always able to act through a channel on a part of the valve body. A vent bore, which guarantees that the internal pressure is always greater than the atmospheric pressure prevailing behind the valve, is provided for this purpose between the valve body and the stopper. So that this pressure gradient can always be maintained, there must a connection to the atmosphere via the vent bore, which must be located behind the seal. The need to introduce an axially oriented vent bore in the piston rod calls for complicated manufacturing operations.